Electric gaseous discharge device



April 14, 1936. R MAXTED 2,037,387

' ELECTRIC GASEOUS DISCHARGE DEVICE I Filed Feb. 5, 1935 INVI ENTOR W W BY 0M? 5. A 1" ORNEY Patented Apr. 14, 1936..

PATENT OFFICE 2,037,387 ELECTRIC GASEOUS DISCHARGE DEVICE Robert Maxted, Rugby, England, assignor to "General Electric Company, a corporation of New York Application February 5,- 1935, Serial No. 5,107 -In Great Britain February 16, 1934 6 Claims. (Cl. 176-124) The present invention relates to electric gaseous discharge devices, and in particular to devices which operate with a high intensity constricted arc discharge.

A particular object of the invention is to provide means to control the path of a constricted are discharge. A further object of the invention is to provide means whereby an electric gaseous discharge device may be operated with a constrictedv arc discharge in a horizontal direction. Another object of my invention is to provide a novel means for controlling the are which will compensate for changes in the arc current during different periods of operation. Still other objects and advantages of the invention will appear from the following detailed specification, or from the accompanying drawing.

The invention consists in the new and novel combination of elements which is hereinafter set forth and claimed.

In operating gaseous electric discharge devices, such as the recently developed high intensity mercury vapor lamp, wherein there is a constricted arc discharge, difficulties are encountered whenever an attempt, is made tooperate the device with the are operating in other than a vertical line. These difliculties are caused by the fact that the arc tends to rise, due to the heating of the gas in the arc stream, and thus curves upwardly and impinges upon the upper wall of the arc tube as the latter is moved toward a horizontal posievolving copious amounts of gas into the discharge path, either of these effects alone being enough to ruin the discharge device. It has been proposed heretofore to overcome this difiiculty by the use of a magnetic force which opposes this upward movement of the arc stream, and in practice it has been found that this gives very desirable results. A lesser difliculty still remains, however. Thus during the starting period of one of these high intensity mercury vapor arc lamps the arc current is quite high, of the order of double that which flows after the vapor pressure has reached equilibrium, and. hence the series magnets which have been heretofore used exert a downward force on the are which is of the order of four times that which is exerted during the normal operation of the lamp. At the same time the temperature of the arc stream is still less than that attained during operation so that the gravitational forces which tend to force thearc upwardly are much less than those which the magnetic force is designed to neutralize. As a result it is found that a magnetic field which is entirely satisfactory during continued operation of a lamp will force the arc downwardly onto the lower wall of the arc tube during starting, failures occasionally occurring as the result of the abnormal heating to which the envelope wall is thus subjected.

I have now discovered that this difficulty is entirely overcome by providing a magnetic field whose intensity decreases as the arc current in- I creases. This novel result may be produced in a number of ways, such as by using a magnet which is connected in parallel with the are, or by utilizing the differential between a series connected magnet and one whose current remains constant or even decreases with increases in arc current. These various arrangements produce changes in either the strength or phase, or both, of the magnetic field which I have found to be sufficient to maintain the arc at the axis of the envelope at all times. Where more than one coil is employed they can be mounted on either a single or separate cores, as desired, so long as the fields thereof merge to provide a fairly uniform density along the arc path, it being noted that somewhat less density is ordinarily required at the center of the arc than at the ends thereof for the best operation, and that my invention contemplates such a departure from an absolutely uniform field.

For the purpose of illustrating my invention I have shown several embodiments thereof in the accompanying drawing, in which Fig. 1 is a schematic diagram of a preferred circuit for horizontal operation of a high intensity vapor arc lamp,

Fig. 2 is a schematic diagram of a modification of this circuit, and

Fig. 3 is a schematic diagram of a further modification of the circuit of Fig. 2.

Referring to these figures there is schematically shown in each an arc discharge device I of the type disclosed, for example, in U. S. Patent 1,948,261 to Francis. These devices, which are now going into extensive commercial use, are well known, and since the structure thereof forms no part of this invention they have been only schematically illustrated. It may be noted however,

that these devices have an inner envelope which contains a gas, such as argon, at a low pressure plus a quantity of a substance, such as mercury, which will be entirely vaporized at the normal op-- erating temperature. Thermionic cathodes are provided at opposite ends of this envelope. In general the inner envelope is enclosed within an outer heat conserving jacket, and the space between the envelope and jacket may be either evacuated or filled with a desired atmosphere, such as nitrogen at a pressure of say half an atmosphere.

In this type of device the discharge is first initiated, with the assistance of external or internal auxiliary electrodes if desired in the gas fill- ,ing. This discharge then heats the mercury causing the vapor pressure thereof to increase until the discharge becomes a characteristic low pressure mercury vapor arc, operating with high current and low voltage. The mercury vapor pressure continues to increase, however, as a result of the heat produced by this discharge, and with this increase in vapor pressure the are becomes more and more constricted, and at the same time the arc voltage rapidly increases, while the arc current decreases, until all. the mercury is evaporated and the stable operating condition is attained. It is this great variation in the arc current during starting that has caused the greatest difiiculty in controlling the position of the arc by means of a magnetic field, for when series coils are used, as heretofore, as being the most convenient way to obtain the proper phase relation with the arc current, the magnetic reaction is excessive during this starting period. This forces the arc downwardly into contact with the bottom of the envelope and thus causes damage thereto.

Fig. 1 shows one way in which I have overcome this diificulty. As shown in this figure the lamp I is connected in series with the usual arc stabilizing inductance 2 and a series coil 3 across a suitable source of current, such as 220 volts A. C. A second magnet coil 4 is connected directly across said source. The coils 3 and 4 are preferably both mounted on the same core 5 in such a position as to produce the desired uniformity of flux through the lamp I in a direction at right angles to the axis of said lamp. While shown as displaced axially for simplicity of illustration it is to be understood that the coils 3 and 4 may be superimposed, and that the best results are attained thereby. It is also to be understood that in some cases these coils can be mounted on separate cores, in which case the core of the magnet 3 may be made saturable by less than the starting current, so as to minimize the change in the fieldproduced by this coil. These coils and their core are located above the lamp I, in case the light distribution is to be mainly downward, or slightly at one side where the light is to be distributed mainly to the opposite side, and are supported in any suitable manner, as by the reflector which is commonly used. The coils 3 and 4 are so connected that they oppose each other, the field produced by the coil 4 being slightly stronger than that produced by the coil 3 when the maximum starting current is passing therethrough and being in a direction to force the arc stream downwardly. This arrangement, of course, provides a much greater predominance of the field due to coil 4 after the arc current has decreased to its normal value. By suitably ad-- normally, and suitable means, such as a condenser is inserted in the shunt circuit, if necessary to correct the phase relation of the current therein to produce this result.

In this circuit it is obvious that the field produced. by the coil ,4 remains constant while that produced by the coil 3 is very large at the start but decreases as the mercury vapor pressure within the lamp I increases. The resultant field produced by these coils is thus relatively small so long as the arc current is high, so that there is no tendency to force the arc stream downwardly onto the bottom of the lamp I. This result is further enhanced by the fact that the phase of the arc current is somewhat shifted during this starting period, so that the mutual reaction between the arc current and the field is even further reduced than would be indicated by the absolute values of these factors. As the are current decreases, however, the resultant field gradually increases and the phase relations also improve, so that the magnetic force is autome tically adjusted to maintain-the arc stream at the axis of the lamp I.

While I have shown one of the coils as connected in series with the lamp I it is to be understood that the same result may be obtained in other ways, such as by connecting this coil in parallel with the inductance 2, so long as the current fiow is a function of the aarc current.

In Fig. 2 a single coil 6 is used to control the position of thearc. This coil is connected in series with a resistance I and a condenser 8 across the terminals of the lamp I, and is placed above the lamp I so as to depress the arc therein. The resistance 7 is used to limit the current to a desired small value in case there is not suflicient resistance in the coil 6, and to reduce the effect of temperature changes in the resistance of said coil, while the condenser 8 is made of such a'value that the current in this shunt circuit is in phase with the current through the lamp l.

With this novel circuit the current through the coil 6 is always proportional to the voltage across the lamp I, and as hereinbefore noted this are voltage is low whenever the arc current is high. Hence this structure provides another means of reducing the field strength during the period of high current flow as the arc is started, so that the arc is automatically maintained at a central point within the lamp I regardless of variations in the arc current.

When a still greater variation in field strength is desired this can be attained by adding to the structure of Fig. 2 a coil 3 which is connected in series with the lamp I, as shown in Fig. 3. In this case the field producced by the coil 3 is made to oppose, but never to equal, the field produced by the coil 6. With this structure a. variation in the arc current produces a very marked change in the resultant field, due to the fact that the component fields change in opposite directions. Thus as the arc current decreases from its high starting value the dominating field of coil 6 increases, due to the increase in are potential, while the subtractive field due to coil 3 decreases directly with the current. As a result there is an exceptionally rapid increase in the resultant field which is available to control the arc position within the lamp I.

In each of these cases the coils are preferably located above the arc, since this has been found to give a greater stability of action. This is due to the fact that any excess in field strength auto matically moves the are further from the coils ture.

' it is to be understood that it is not limited thereto, but that various omissions, substitutions and changes, within the scope of the appended claims, may be made therein without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:-.

1. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field therein varying as an inverse function of the current through said device whereby a discharge between said electrodes is maintained in a desired position within saiddevice.

2. In combination, an; electric gaseous discharge device comprising a sealed envelope containing a vaporizable material which provides the operating gaseous atmosphere and having electrodes sealed therein, an impedance connected in series with said device, and means to produce a magnetic field within said device to controlthe position of a discharge therein, said means being connected in parallel with said device, whereby the intensity of said field varies as an inverse function of the discharge current between said electrodes.

3. In combination, an electric gaseous discharge device comprising a sealed envelope containing a vaporizable material which provides the operating gaseous atmosphere andhaving electrodes sealed therein, and means to produce a magnetic field within said device to control the position of a discharge therein, said means comprising a pair of coils the composite field of which is an inverse function of the discharge current between said electrodes.

4. In combination, an electric gaseous discharge device comprising a sealed envelope containing a vaporizable material which provides the operating gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of a discharge therein, said means comprising a coil which is traversed by a current which is a direct function of the discharge current between said electrodes and a second coil which is traversed by a current which does not change in the same direction as the arc current, the fields produced by said coils being opposed.

5. In combination, an electric gaseous discharge device comprising a sealed envelope containing a vaporizable material which provides the operating gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of a discharge therein, said means comprising a coil which is connected in series with said discharge device and a second coil which is connected to a fixed source of potential, the fields produced by said coils being opposed.

6. In combination, an electric discharge device comprising a sealed envelope containing a vaporizable material which provides theoperating gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of a discharge therein, said means comprising a coil which is connected in series with said discharge. device and a second coil which is connected in parallel with said discharge device, the fields produced by said coils being opposed.

ROBERT MAXTED. 

